The present invention relates generally to an imaging apparatus in which a plurality of photosensitive chips are mounted on a substrate. In particular, the present invention relates to a signal processing method which addresses uneven chip-to-chip gaps in such an apparatus.
Image sensors for scanning document images, such as charge coupled devices (CCDs), typically have a row or linear array of photosensors together with suitable supporting circuitry integrated onto a silicon chip. Usually, a sensor is used to scan line by line across the width of a document with the document being moved or stepped lengthwise in synchronism therewith. A typical architecture for such a sensor array is given, for example, in U.S. Pat. No. 5,153,421.
In one design of a full-page-width image scanner, there is provided a linear array of small photosensors which extends the full width of an original document, such as 11 inches. These photosensors may be spaced as finely as 600 to the inch on each chip. When the original document moves past the linear array, each of the photosensors converts reflected light from the original image into electrical signals. The motion of the original image perpendicular to the linear array causes a sequence of signals to be output from each photosensor, which can be converted into digital data.
A currently-preferred design for creating such a long linear array of photosensors is to provide a set of relatively small semiconductor chips, each semiconductor chip defining thereon a linear array of photosensors along with ancillary circuit devices. These chips are typically approximately xc2xe inches in length; in order to create a practical full-page-width array, as many as twenty or more of these chips can be placed end-to-end to form a single linear array of photosensors. The chips are typically mounted on a support platform. This support platform also includes circuitry, such as on a printed wiring board, which accesses the circuit devices on the individual chips for a practical system. The interconnections between the relatively large-scale conductors on the printed wiring board and the relatively small contact pads on the semiconductor chips are preferably created by wire bonds which are ultrasonically welded to both the printed wiring board conductors and to contact pads on the chips.
When the chips are mounted within an imaging apparatus, such as a document scanner, the imperfections of each chip combine with the imperfections of the mounting process to yield an overall problem of unpredictably-sized gaps between each adjacent pair of chips in the array, and more specifically, unpredictably-sized gaps between neighboring photosensors on neighboring chips. As the chip collectively form one or more continuous linear arrays of photosensors when assembled, the presence of a plurality of gaps in the linear array will have profound effects on the quality of images recorded with the scanner. Various techniques have been proposed in the prior art, such as described in detail below, to take into account these unpredictably-sized gaps as they effect the regularity of spacing of photosensors along a complete linear array. These techniques largely comprise taking actual measurements of the gap between each pair of chips (such as by recording a test pattern, for example), retaining the calculated measurements of each gap, and then, when the scanner is used for recording images, compensating for each specific gap width using, for instance, an interpolation technique based on the readings from photosensors adjacent each gap.
The present invention is directed to a method of compensating for unpredictably-sized gaps along a linear array of photosensors, which uses a simple algorithm and does not require either testing of, or retention of specific information about, individual gaps along the array.
U.S. Pat. No. 5,552,828 discloses a page-width linear array comprising a plurality of chips. Imprecisions associated with inter-chip gaps are remedied by providing end photosensors with trapezoidal or near-trapezoidal geometries.
Japanese publication JP 09-321948-A discloses a maintenance method for a scanner in which the sizes of inter-chip gaps in a scanner are measured by scanning an image of a perfect circle and analyzing the resulting image.
Japanese publication JP 10-126584-A discloses a maintenance method for a scanner in which the sizes of inter-chip gaps in a scanner are measured by scanning an image of a series of angled lines and analyzing the resulting image.
Japanese publication JP 2000-196835-A discloses an operating method for a scanner in which the sizes of specific inter-chip gaps in a scanner are retained in memory, and subsequent image signals are interpolated based on the retained gap sizes.
Japanese publication JP 2000-199702-A discloses a maintenance method for a scanner in which the sizes of inter-chip gaps in a scanner are measured by scanning an image of a series of lines and analyzing the resulting image.
According to one aspect of the invention, there is provided a method of processing image data from a photosensitive imaging apparatus, the apparatus including a plurality of chips, each chip having a linear array of photosensors thereon, the photosensors on each chip being spaced by a predetermined pitch, each photosensor adapted to output a value related to light incident thereon, the chips being mounted with the linear arrays thereon arranged to form a main linear array, each pair of chips in the plurality of chips defining a gap therebetween. For a chip, the outputs of the photosensors therein are interpolated to effect a spatial displacement of the outputs along the main linear array. The displacement is a product of a constant and an integer, the integer relating to a position of the chip along the main linear array.
According to another aspect of the invention, there is provided a method of processing image data from a photosensitive imaging apparatus, the apparatus including a plurality of chips, each chip having a linear array of photosensors thereon including an end photosensor, the photosensors on each chip being spaced by a predetermined pitch, each photosensor adapted to output a value related to light incident thereon, the chips being mounted with the linear arrays thereon arranged to form a main linear array, each pair of chips in the plurality of chips defining a gap therebetween. For a chip, an output is interpolated of a phantom photosensor disposed a predetermined distance from an end photosensor toward the gap, thereby yielding an artificial value. The artificial value is added to a data stream output from the chip.